The present invention relates to a catheter, and in particular, though not limited to a measuring catheter, such as, for example, a catheter having two or more measuring electrodes located at spaced apart intervals on the catheter or a balloon catheter comprising an elongated catheter having an inflatable element located on the catheter and two or more measuring electrodes located within the inflatable element on the catheter. The invention also relates to a system and a method for locating a catheter in a vessel in a human or animal subject.
Catheters for measuring cross-sectional area, diameter, as well as volume of a vessel in a human or animal body are well known. Such catheters may comprise an elongated catheter having two or more, and typically a plurality of measuring electrodes longitudinally spaced apart along the catheter towards a distal end thereof. Typically, two of the electrodes are stimulating electrodes to which a stimulating current of constant known value is applied, and the remaining electrodes which are located between the stimulating electrodes are sensing electrodes. When the portion of the catheter with the measuring electrodes thereon is located in a vessel, and the vessel is filled with an electrically conductive medium, voltages are induced on the sensing electrodes when the stimulating current is applied to the stimulating electrodes. The voltages induced on the sensing electrodes are indicative of the cross-sectional area and the diameter of the vessel adjacent the respective sensing electrodes. If the vessel is assumed to be of circular transverse cross-section, the voltage signal induced on the sensing electrodes are indicative of the diameter of the vessel. From these voltage values the cross-sectional area and the diameter of the vessel adjacent the respective sensing electrodes can be computed as well as the volume of the vessel. Typically, such catheters are used for measuring the diameter, cross-sectional area or volume of a relatively narrow vessel, such as, for example, an artery or the like.
Another type of measuring catheter is a balloon catheter which comprises an elongated catheter having an inflatable element, typically a balloon located on the catheter towards the distal end thereof, with the catheter extending through the balloon to define with the balloon an annular hollow interior region. Measuring electrodes similar to those described with reference to a measuring catheter are provided on the catheter within the balloon. Such balloon catheters are generally used for determining the cross-sectional area, diameter and the volume of a larger vessel in the human or animal body, for example, the stomach, the oesophagus, the rectum, intestine, the bowel or the like, and are also commonly used in procedures known as bariatric surgery as well as anti-reflux surgery to correct gastro-oesophageal reflux disease. To determine the diameter, cross-sectional area and/or volume of a vessel, the balloon of the balloon catheter is placed in the vessel, and the balloon is inflated with an electrically conductive inflating medium to fill the vessel. By applying a constant current of known value through the stimulating electrodes, voltages induced on the sensing electrodes are indicative of the diameter and cross-sectional area and the diameter of the vessel adjacent the respective sensing electrodes.
One problem which arises with such catheters, be they measuring catheters without a balloon or measuring catheters with a balloon, namely, balloon catheters, is that, in general, it is relatively difficult to locate the balloon, or in the case of a non-balloon catheter, the portion of the electrodes accurately in the vessel, the diameter, cross-sectional area or volume of which is to be determined, or monitored. For example, during bariatric surgery and anti-reflux surgery it is difficult to accurately locate the balloon of a balloon catheter in the stomach or the lower oesophageal sphincter, as the case may be, with the sensing electrodes accurately located relative to the lower oesophageal sphincter and the stomach.
Additionally, catheters and balloon catheters having one or more spaced apart ablating electrodes on the catheter of an ablating catheter, and on the external surface of the balloon in the case of an ablating balloon catheter, are used for ablating tissue in a lumen or vessel. It is also in many cases difficult to locate such catheters and balloon catheters in the vessel or lumen with the ablating electrodes accurately aligned with the tissue to be ablated.
There is therefore a need for a catheter and a balloon catheter which addresses these problems.
The present invention is directed towards providing such a catheter; the catheter may be a balloon catheter or a non-balloon catheter, and the invention is also directed towards providing a system and a method for locating a catheter, be it a balloon catheter or a non-balloon catheter, in a vessel.